Network Research Group
University of California, Irvine.

x-kernel
Object-based framework to implement network protocols; defines an interface that protocols use to invoke operations on one another (i.e., to send messages to and receive messages from adjacent protocols) and a collection of libraries to manipulate messages, participant addresses, events, associative memory tables (maps), and threads.

KA9Q NOS TCP/IP Package
Second known implementation of Internet protocol (IP) for low-end computers; can at once be network client, server, IP packet router; support multiple client and server sessions. Description, downloads, zip format. Original author.

Systems Research Group, Networks and Operating Systems
University of Cambridge, Computer Lab. Many interesting network OS oriented projects, including Nemesis OS.